Interconnecting rotary and reciprocating motion

ABSTRACT

A pair of opposed pistons (17) are interconnected by a connecting link assembly (19) defining opposed parallel guide surfaces (24), transverse to the axes of the pistons. A drive block (28) is rotatably mounted on a crankpin (16) of a crankshaft by a bearing shell (71a, 71b) and has parallel bearing plates (31) slidably engaged with the guide surfaces (24). Lubricating oil is supplied to ports (59) in the bearing plates, just before each plate is substantially loaded, from leading and trailing drillings (56L and 56T) in the crankpin (16), ports (76, 77) in the bearing shell and passages (73, 74, 75) in the drive block.

FIELD OF THE INVENTION

The present invention relates to apparatus for converting reciprocatingmotion to rotary motion and vice-versa comprising a reciprocatoryassembly guided for reciprocation in a first direction and comprisingfirst and second reciprocating members each terminating in a planarguide surface transverse to the direction of reciprocation, and spacingtie means interconnecting the two reciprocatory members at opposite endsof the guide surfaces to maintain the guide surfaces parallel, spacedapart and facing each other, a drive block having opposed guide faceseach slidably engaged with a respective one of the guide surfaces of thereciprocatory members, a rotary member mounted for rotation about anaxis transverse to the said direction of reciprocation and having aneccentric portion rotatably engaged in a plain bearing in the driveblock and a lubrication system for supplying lubricant under pressurethrough the rotary member to a plurality of outlet ports in the surfaceof the eccentric portion, the drive block having a passage leading tothe respective guide surfaces from respective ports in the plain bearingpositioned to communicate with the outlet ports of the eccentric portionas the latter rotates in its bearing.

BACKGROUND OF THE INVENTION

Such apparatus as described above is particularly suitable forinterconnecting a pair of opposed pistons with a crankshaft throw inpositive fluid displacement machines such as pumps and internalcombustion engines as proposed for example in EP-A 0,241,243.

A problem in such known apparatus is to ensure adequate lubrication theplanar guide surfaces under the high loads imposed on them particularlyat high speeds.

Apparatus according to the invention is characterised in that thebearing port or ports connected with a guide surface lie within aquadrant of the plain bearing, the two quadrants being on opposite sidesof the axis of the bearing, and the outlet ports in the eccentricportion all lie in a sector thereof smaller than the angular extent ofthe unported portion of the bearing separating ports connected todifferent guide surfaces of the drive block.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described by way of examplewith reference to the accompanying drawings, in which:

FIG. 1 shows schematically and mainly in section an internal combustionengine according to the invention as seen from the end adjacent thetiming gears and chains;

FIG. 2 is a plan view, mainly in section on the line II--II of FIG. 1;

FIG. 3 is a sectional view on the line III--III of FIG. 2, on anenlarged scale;

FIGS. 4a to 4h each show the crankpin bearing portion of FIG. 3 on anenlarged scale in eight successive positions during half a revolution ofthe crankshaft; and

FIG. 5 is a plan view of a modified drive block bearing plate.

DETAILED DESCRIPTION

FIGS. 1 and 2 show diagrammatically the-principal components of aneight-cylinder horizontally-opposed internal combustion engine havingtwo banks of four cylinders each. The cylinders C1, C3, C5 and C7 arearranged in line in one bank A while the other cylinders C2, C4, C6 andC8 are arranged in line in the other bank B. Each cylinder is formed bya cylinder liner 11 mounted in an engine block 12, the lower end ofwhich is closed in the normal manner by an oil sump 13.

Each pair of opposed cylinders, such as C1 and C2, are coaxial. A rotarymember or crankshaft 14 is rotatably mounted in five main bearings 15 inthe engine block 12 end has four eccentric portions, i.e. crankpins 16,one for each opposed pair of cylinders. Measured in the direction ofrotation of the crankshaft 14, the angular spacings of the crankpins 16are, from the front of the engine (i.e. the left hand side in FIG. 2)0°, 180°, 270° and 90°. Thus, the firing order for the engine in fourstroke form is 1-6-3-8-4-7-2-5.1.

Each cylinder contains a piston 17. The two pistons 17 of a pair ofopposed cylinders such as C1 and C2 are connected together by areciprocatory connecting assembly shown on an enlarged scale in FIG. 3.

Each connecting assembly consists of a connecting link (18A,18B) foreach piston and four connecting plates 19 which are each of a U-shapedformation. Each connecting link 18 has a spigot 20 at one end whichengages in a bore in its associated piston 17 and is itself formed witha screw threaded bore to receive a bolt 22 securing the piston to theconnecting link. Each bolt 22 has its head located in an aperture in thepiston crown and this aperture is subsequently closed by a plug 23screwed into the centre of the piston.

At its other end, each connecting link 18 widens out to form a longrectangular flat guide surface 24 which is surface-hardened, for exampleby nitriding. The connecting links 18 are stiffened by appropriate ribsin the form of two outer ribs 25 and a central rib 26, with spacesformed in between the ribs by web portions 27.

A drive block 28 is formed in two halves 28a and 28b which are securedtogether by screws 29 and are-accurately located relative to each otherby tubular dowels 30. In opposite faces of the drive block 28 arelocated bearing plates 31 of appropriate bearing-forming material toslidably engage the guide surfaces 24. Movement of the bearing plates 31relative to the drive block 28 in the direction along the drive block isprevented by transverse ribs 32 formed at the comers of the drive block.

The two connecting links 18 are secured with their guide surfaces 24 atthe correct distance apart by the connecting plates 19 which alsoreinforce the connecting links against deformation in operation. Forthis purpose each connecting plate 19 is formed with a rib 33 engaged ina corresponding groove 34 extending along each lateral face of theconnecting link 18. The connecting plates 19 are secured to theconnecting links 18 by screws 35 having their heads located in counterbores in one connecting plate and having screw threaded portions attheir other ends engaged in screw threaded holes in the opposite plate.

The connecting plates 19 have flange portions 36 which extend inwardlyfrom the guide surface 24 towards each other. These flange portionsincrease the rigidity of the connecting links 18 in the region of theguide surfaces and are themselves surface-hardened to form lateral guidesurfaces for the drive block 28 and its bearing plates 31. The flangeportions 36 bound the parallel sides of a reentrant 37 having asemi-circular end 38. A reentrant 37 provides clearance for the portionsof the crankshaft web immediately adjacent the crankpin 16.

The stiffness of the connecting plates 19 is increased by increasing thethickness of the connecting link portions 39. The distance between theconnecting portions 39 on opposite sides of the central plane is reducedby shaping the crankpin 16 between the two plates at each end as shownin FIG. 2. Thus, the radially outermost portion 16x of the crankpinprojects radially beyond the radially outer portions of the crankshaftwebs 41 and 42. By reducing the distance between the connecting portions39 of the plates 19, the bending moments in the guide surface portionsof the connecting links are further reduced.

As can be seen from FIG. 3, even in the extreme position of its travelalong the guide surfaces, the drive block 28 always has some portion onthe centre line of the reciprocatory assembly.

Turning again to FIGS. 1 and 2, it will be seen that each bank ofcylinders A,B has a respective cylinder head 43A, 43B forming combustionchambers for the cylinders. Each combustion chamber has two inlet valves44a and 44b and an exhaust valve 45. The cylinder heads may be formedwith separate inlet ducts 46a and 46b leading to the respective inletvalves or a single inlet duct supplying both valves may be used instead.Where the engine is a spark-ignition engine, each combustion chamberwill include a-spark plug and the inlet manifold branches (not shown)supplying the inlet ducts will include fuel injectors.

The valves 44 and 45 are operated by a camshaft in each cylinder head,the camshafts being of the "single overhead" type operating valvesthrough rocker arms (not shown). The camshafts are themselves driven athalf crankshaft speed by roller-chains 48A and 48B on sprockets drivenby respective timing gears 49A and 49B meshing both with a gear 50 onthe front end of the crankshaft 14.

Also mounted on the front end of the crankshaft 14 is a helical gear 51meshing with a gear 52 on a shaft 53 driving an oil pump 90 (FIG. 1)which draws oil from the sump 13 and supplies it under pressure to themain bearings 15. Internal drillings 54, 55, 56L and 56T in thecrankshaft supply oil from the main bearings to the crankpin bearings inthe drive blocks. The drillings 56, 56L and 56T extend at 45° to aradial plane through the crankshaft and crankpin axes.

As can be seen in FIG. 4a, the crankpin bearing is formed in the usualmanner by two shell halves 71a and 71b which meet at the dividing planebetween the two drive block halves 28a and 28b. Machined into each driveblock half are arcuate recesses 73a and 74a in respect of the block half28a and 73b and 74b in respect of the block half 28b. The recesses areof approximately the same axial width as their radial depth. Each recess74 leads into an inclined drilling 75 (75a for drive block half 28a and75b for drive block half 28b), the recesses 73 and 74 forming onecontinuous arcuate recess which connects to the respective inclineddrilling 75. The outlet of each drilling 75 registers with an oildelivery hole 59 in the centre of the bearing plate 31.

Each hearing shell half 71a and 71b is respectively formed with arelatively long window or opening 76a, 76b extending over 35° and whichis spaced from the end of the shell half by 10°. Spaced from the otherend of each shell half by 10° is a shorter window or opening 77a, 77bsubtending an angle of 15° at the centre of the crankpin. Thus, betweenthe two openings 76 and 77 there is an uninterrupted bearing shellportion subtending an angle of 110°. The majority of this portion is indirect contact with the more highly loaded parts of the drive block, therecesses 73, 74 being formed in the portions which receive littleloading transversely of the reciprocating assembly.

FIG. 4a shows-the position in which the piston 17 in FIG. 3 would be atbottom dead center while the piston which would be attached to the lowerend in FIG. 3 would be at top dead center. In this position, thecrankpin is accelerating the reciprocating assembly of connecting rodsand pistons upwardly. The leading drilling 56L is now in communicationwith the drilling 75a by way of the opening 76b and the recess 73b, 74a.Although the upper surface of the drive block is loaded, this enablesany necessary preliminary filling of the recess and drilling 75a to becompleted as the motion continues to the position shown in FIG. 4b.

In the position shown in FIG. 4c, the leading drilling 56L has beenclosed off by the adjacent solid portion 78b which necessary to preventloss of oil laterally in the axial direction at the interface betweenthe two shell halves.

In the position shown in FIG. 4d, the leading drilling 56L is again incommunication with the drilling 75a through the opening 77a.

In the position shown in FIG. 4e, the drive block has reached theposition which is effectively the mirror image of that shown in FIG. 3and the vertical acceleration is now zero. Under its inertia, thereciprocating assembly moves upwards in the figure and begins to berestrained or accelerated downwards by the crankpin. This tends to openthe small clearance between the planar guide surfaces of the guide blockand the guide surface 24, and at the same time, the trailing drilling56T is nor in communication with the drilling 75a (FIGS. 4e and 4f).Under the pressure from the lubricating system augmented by thecentrifical head generated within the rotating crankshaft, oil issupplied under pressure to fill the clearances in the planar bearing onthe upper side of the drive block. In FIG. 4g this is temporarilyinterrupted as the trailing drilling 56T passes across the portion 78bof the shell halves. Finally in FIG. 4h, both drillings are closed off.

It should be noted that throughout the range of movement illustratedfrom FIG. 4a to FIG. 4h, the lower drilling 75b has been continuouslycut off from the oil supply. This prevents any risk of loss of oil fromthis drilling 75b across to the drilling 75a.

The upper bearing is now fully charged with oil just in advance of thetime in which it is to be subjected to its maximum load.

FIG. 5 shows a modified form of drive block bearing 131 having more thanone oil delivery hole, in this case two delivery holes 159 positionedrespectively one third and two thirds of the distance from one end ofthe plate to the other, with a view to improving the supply anddistribution of oil over the whole working area of the bearing plate.Each delivery hole 159 is conveniently supplied with oil from the driveblock recess (74a or 74b) by a separate drilling in the drive block.

Distribution may also be improved by the use of grooves 160 formed inthe working surface 161 of the bearing plate and communicating with thefeed hole 59 or feed holes 159.

We claim:
 1. An apparatus for converting reciprocating motion to rotarymotion and vice-versa, comprising a reciprocatory assembly guided forreciprocation in a first direction and comprising first and secondreciprocating members respectively terminating in first and secondplanar guide surfaces which extend transverse to the direction ofreciprocation, and spacing tie means interconnecting the tworeciprocatory members at opposite ends of the guide surfaces to maintainthe guide surfaces parallel, spaced apart and facing each other, a driveblock having opposed guide faces each slidably engaged with a respectiveone of the guide surfaces of the reciprocatory members, a rotary membermounted for rotation about an axis transverse to said direction ofreciprocation and having an eccentric portion rotatably engaged in aplain bearing in the drive block, and a lubrication system for supplyinglubricant under pressure through the rotary member to a plurality ofoutlet portions defined in a surface of the eccentric portion, the driveblock having a respective passage leading to the respective guide facefrom a respective window in the plain bearing and positioned tocommunicate with the outlet ports of the eccentric portion as the latterrotates in said bearing, wherein each said window in the bearing lieswithin a quadrant of the plain bearing, two said quadrants eachcontaining a said window being on opposite sides of the axis of thebearing, and the outlet ports in the eccentric portion all lie in asector thereof smaller than the angular extent of an unported portion ofthe bearing which separates the windows as connected to different saidguide faces of the drive block.
 2. An apparatus according to claim 1,wherein said eccentric portion has two said outlet ports spaced about90° from each other.
 3. An apparatus according to claim 1, wherein saideccentric portion has two said outlet ports in a radially outer regionthereof relative to an axis of rotation of the rotary member, the outletports lying on opposite sides of a plane through the axes of the rotarymember and the eccentric portion thereof.
 4. An apparatus according toclaim 1, wherein the drive block and the plain bearing are divided intotwo equal halves at a plane through an axis of the eccentric portion,the plain bearing halves each having a said window near, but spacedfrom, each end thereof and the drive block has for each guide face asupply passage leading from and connected to one said window of eachbearing half.
 5. A piston and cylinder machine having at least one pairof opposed pistons on opposite sides of a rotary member in the form of acrankshaft, wherein the pistons of said pair are connected to apparatusas claimed in claim 1.